Many individuals over the age of 40 develop intolerance for milk and milk-based products. A dairy has developed a line of lactose-free products that are more tolerable to such individuals. To
assess the potential market for these products, the dairy commissioned a market research study of individuals over 40 years old in its sales area. A random sample of 250 individuals showed that 86 of them suffer from milk intolerance. Based on the sample results, calculate a 90% confidence
interval for the population proportion that suffers milk intolerance. Interpret this confidence interval.

a) First, show that it is okay to use the 1-proportion z-interval. (Assumptions)

b) calcuate by hand a 90% confidence interval (use the formula)

c) provide an interpretation (conclusion)

d) if the level of confidence was 95% instead of 90% would the resulting interval be narrower or wider? explain. (show your computation before your explanation)

e) if the researchers were interested in the 90% interval with the 3% margin of error what size sample would they require?

f) verify your 90% confidence interval using your calculator.